Polishing is to be understood as a method for the chip-making fine-machining of surfaces employing a geometrically undefined cutting edge, the removal of stock being accomplished by means of a polishing agent composed of unbonded mineral powder, usually metal oxides, with a high melting point and a very low tendency to dissolve in water or oil. For polishing purposes, the mineral powder is reduced to a paste or is mixed with heat-resistant lubricants or paraffins to yield a polishing paste or a polishing-agent suspension.
To produce high-precision functional surfaces on workpieces, the polishing is done on a lapping machine, or, in the case of optical lens fabrication, with a polishing bowl. Such a polishing bowl is usually lined with a polishing-agent support that keeps the polishing suspension on the tool and dictates the final shape of the workpiece surface. Plastic sheeting, felt, pitch or felt flake pitch are used as polishing-agent supports.
For decorative fine-machining of surfaces, the usual approach is to use hand-operated machines with polishing tools that do not have a contour specific to the workpiece and are not intended to shape it. Instead, polishing usually serves in these cases to finish the surface for decorative purposes or to restore it in the repair shop (e.g. refinishing of varnished parts, polishing out of scratches).
Aside from exclusively manual polishing, polishing with hand-guided machines is the most widespread application for producing decorative surfaces or for finishing. A number of polishing tools for this purpose are known, and are designed to be used on machines similar to grinding stands or to be driven by means of hand drills, right-angle grinders or straight grinders.
Known, for example, from the 1998/1999 tool catalogue of the company Hch. Perschmann GmbH, Braunschweig, pp. 462 and 464, are polishing tools in which a one-piece, compact felt body, characterized as particularly long-lasting and offered in a cylindrical, conically tapered or disk-shaped embodiment with a steel shaft 6 mm in diameter, is designed to be gripped in a machine. A suitable grinding paste is also offered for use with these felt polishing bodies.
Known from the catalogue Machinery and Tools for Surface Machining from the firm Suhner Abrasive Expert AG, Brugg, Switzerland, 1998 edition, are solid felt polishing wheels (model designations FPS 30 to FPS 200), which can be used with machines together with holding arbors for attaching the felt polishing wheels (models FDv 6-6 et seq.). Also offered under the designations FPK0708 to FPK3035 is a series of contoured felt polishing bodies that range from small, spherical shapes for the felt through various partially conical forms to cylindrical, solid felt polishing bodies. These felt polishing bodies are also provided with shafts for mounting them in standard drill chucks.
Also known, particularly for use on vehicle bodies before and after painting, are so-called buffing wheels or buffing bells, in which the polishing body of the polishing tool consists of a packet of cotton cloths laid one on top of the other and quilted together according to the desired strength; these are arranged radially to a bore in a work-holding spindle or to the spindle itself.
The basic advantage of such buffing wheels is that there is little transfer of the contour of the tool to the workpiece, so that few marks are likely to be produced even on highly sensitive surfaces, e.g. piano lacquers.
Known from U.S. Pat. No. 3,191,208 are various buffing wheels in some of which the hardness of the wheel is further increased by folding the cotton cloth, and in which, instead of a receiving opening for a mandrel, a pronged metal pot is provided, on whose prongs, which are arranged radially about an attaching opening for connection to a mandrel of a machine, the cloth packet is threaded either with or without additional sewing up or quilting. The prongs are realized as longer than the cloth packet is thick, so that the cloth packet can be fixed in place axially by turning the ends of the prongs down once the packet has been threaded on.
Known from Patent Abstracts of Japan under JP 60094271 is a tool in which a heat-curable resin is poured over individual lengths of polishing cloth comprising a fiberglass disk so as to form an even number of packets composed of two to three plies of cloth, and the packets are arranged shingle-like on the wheel about a central receiving hole for a mandrel. This produces a tool hardness that is extremely unusually high for polishing tools, of the kind exhibited by flap wheels, so that some doubt arises as to whether a polishing tool is really being described here or whether the subject matter is a cloth with an abrasive bonded to it, in the manner of an abrasive cloth, and the tool is therefore an embodiment of the flap wheel that is known per se.
Known from DE 199 30 373 A1 is a porous polishing tool and a method for polishing a roller, designed to enable a roller to be polished to satisfactory dimensional precision and thus to prevent feed marks and streaking when the polished roller is to be used for printing.
Known from DE 198 43 267 A1 is a polishing wheel that includes a short fibrous-web layer firmly bonded to a support layer, and in which a burr-type adherent layer is disposed on the back of the polishing wheel so that it can be fastened removably to a corresponding polishing disk. Cited as an advantage is the fact that the polishing wheel can be removed from the polishing disk and washed in a household or industrial washing machine, thereby removing dried polishing agent and polishing dust. This is intended to allow the polishing wheel to be used several times.
For use with the known polishing tools described hereinabove, a suitable polishing paste must be selected that is adapted to the hardness of the felt material and its porosity, it being especially important for the admixture of lubricant or oil to be such that the polishing tool is prevented from clogging prematurely. Such premature clogging causes streaks and smears on the workpiece and can lead to burn marks in extreme cases.
This problem is reputedly avoided with the polishing wheels described in German Utility Patent DE GM 1 940 005, in which an adapted polishing agent is to be integrated in a soft bond. This is to be achieved by saturating the fabric with the polishing-agent preparation or by embedding the preparation, for example by enveloping it in lengths of cloth. It is emphasized as essential that the textile nature of such a polishing wheel is preserved, as in the case of known polishing wheels composed of flat or puffy layers of fabric.
In addition, as in the case of other polishing wheels, the machinist must maintain the proper contact pressure to achieve the desired polishing action and at the same time prevent overheating. As noted hereinabove, such overheating can lead to burn marks on the workpiece or carbonization of the polishing felt, which can in turn cause the workpiece to become scratched during subsequent use of the polishing tool.
The polishing result therefore depends on a certain degree of experience and dexterity on the part of the machinist, and on his experience in the appropriate selection of a polishing body of suitable hardness and a polishing agent adapted to the workpiece material and the polishing body.
It is therefore desired to provide a polishing tool of the type described hereinabove, having improved characteristics with regard to handling and the achievement of better working results.